This invention relates generally to energy-efficient projectors of electromagnetic radiation which collect energy emitted from a source and, more particularly, to shallow reflector assemblies that efficiently collect light emitted from a light source and project it into a predetermined beam pattern.
A parabolic reflector is often used to collect light emitted by a light source and form it into an approximately collimated beam. The light source is situated approximately at the focus of the parabola and the light beam formed by the reflector exits through a circular or approximately rectangular aperture centered about the parabola's axis and travels in a direction generally along this axis. A portion of the light emerges from this system without ever intersecting the reflector and hence is called stray light. This stray light component represents an inefficiency in collecting the light from the source. For some applications, this stray light may also cause unwanted glare.
It is known that increasing the depth of the parabola can increase the collection efficiency. However, size concerns often prohibit the use of deep parabolic reflectors and the incremental efficiency gains achieved by increasing the parabola's depth diminish as the depth increases.
For example, in an automobile headlamp, the size of the optical assembly is often restricted to a relatively small volume. Because the parabolic reflector is relatively shallow, the light source is located relatively close to the reflector's exit aperture. This results in a large portion of the light emitted by the source being radiated from the exit aperture without being controlled by the reflector. In a typical headlamp, less than 40 percent of the light is collected by the reflector for projection into the beam.
Further, an automobile headlamp must meet certain glare requirements to avoid blinding oncoming drivers. Typically, a lens having generally discrete prismatic regions is located in the aperture to assist in redistributing the beam so that the resulting pattern achieves a certain lateral spread and so that the vertical glare is also controlled. However, this lens adds to the cost and complexity of the headlamp's optical design.
Accordingly, there is a need for a shallow optical assembly that efficiently collects the light from a source and forms it into a desired beam pattern. The present invention satisfies this needs.